Powdered ferrous metals and articles and methods of making the same



' June as, 1960 2,942,334

R. E. BLUE POWDERED FERROUS METALS AND ARTICLES AND METHODS OF MAKINGTHE SAME 1 Filed Jan. 18. 1957 INVENTOR- gay 2;, ,ZZzle.

nited files This invention relates to improvements in particulateferrous metals, more generally referred to as powdered iron, formakingsintered compacts and other articles or products; to productsessentially comprising such particulate ferrous metals; and to methodsof making said products and preparing said particulate metals for usetherein. 7 t

In making porous articles or products by sintering a formed or compactedmass of powdered iron, itis normal to have some iron oxide present inthemass. However, it is also found that such iron oxide when present on thesurface area of the ferrous particles is detrimental in that itsubstantially inhibits sintering and the obtaining of agoodmetallurgical bond between adjacent particles of the mass duringsintering. Such has been true for example Where the weight loss due to.oxides as determinedby MPA specification 2- 48- hydrogen loss method isin excess arm Certain iron particles for instance, low cost, low gradetype iron particles for example those known commercially as mill scaleor magnetiteand made by reducingdron oxide in a hydrogen atmosphere,inherently contain iron oxide at their center and at the surface areasthereof, These and other iron powders, such as electrolytic ironpowders, also "obtain. such 'iron[ oxide on ,their surface ai 'eas byexposure, prior to briquetting and.especially du r-.

' ing storage, to oxidizing influences such as air, which producecompletely oxidized areasontheparticles. A similar action occurs duringthe early stages of sintering. In many instances these areas extend overthe greater part of the particles and exist as a heavy layer.

, Where these conditions heretofore existed, it has been atent l ice Ihave further discovered that if the ferrous particl are provided withsuch iron sulfide films or layers dur ing the making thereof or at anearly period after their making, it is possible to obtain optimumcoverage of the particles with the iron sulfide and preferably obtain asubstantial envelopment of the particle with films of iron sulfidebefore a complete iron oxide layer is produced on the particles byexposure to air or other oxidizing influences. This layer of ironsulfide will thereafter protect the under surface of the particlesduring storage from oxidizing influences and during sintering up to thetemperature at which coalescence occurs.

Accordingly, the principal object of this invention is to so treatparticulate ferrous metals prior totheir use in the making of sinteredarticles to provide them with surface'portions or films of iron sulfidecapable of having a scavenging actionon iron oxide during the sinteringof compacted masses of such particles and effect a coalescence of theiron sulfide and iron oxide of adjacent particles to form particleboundaries of pure grain character and of iron oxysulfide to enhance themetallurgical bond between adjacent particles. v

Another object is to carry out the treatment set forth in the precedingobject at the time the particulate ferrous materials are-formed, orshortly thereafter, whereby to inhibit the conversion of pure iron oftheparticle'sur faces to iron oxide and thereby inhibit formation ofexcessive surface iron-'oxide'on the particles. I 7

Another object is to provide particulate ferrous material as describedin the preceding objects whichfwill provide in siutered. articles madetherefrom many favorable characteristics including uniformly highphysicalfound essential in order to obtain a satisfactory bonded theresultant products have usually had a lower ultimate strength andductility than in cases where the oxide condition is not present andtheir lack of uniformity in duc- I tility and yield strength have causedrejections. Furthermore, they have left much to be desired by way offacilitating machining and coining.

' Among other reasons why sintered iron products have been desirablecommercially has been the cost savings possible by combining powdermetallurgy and finish machining. In some applications sintered partsmade from low grade iron powders do not have machining characteristicswhich make this combination attractive. I I 'I'have discovered that someof the surfacev iron oxide of the iron particles presently considereddetrimental, canbe advantageously employed to improve sintering, toobtain a better metallurgical bond between the particles, to improve thephysical properties'of the resultant sintered product. I accomplish thisby providing surface areas or films of iron sulfide on the particleswhich in sintering will have a scavenging effect upon the iron oxide at.the surfaces of the particles by forming a liquid phase therewith, i.e.coalescing with or absorbing this iron oxide of adjacent particles toproducean iron oxysulfide properties, good ductility, easy'machinability," anda yield strength which facilitates sizing andcoining'operations andtheobtaining by the latter of ultimate strengthshigher than those .n'ormally expected where the particles did notcontain the advantageous iron sulfide in their surface portions. 1

A particular object isto treat particles'of low cost, low grade ironsuchas mill scale, in a manner to'pro- 'vide on them surface areasofiron sulfide whereby 'to inhibit the production on such particles ofcompletely oxidized areas of: the underlying pure iron by oxidizinginfluences subsequent to theirinitial formation and during storage. 7

Another object is to provide particulate ferrous metals of the characterof the preceding objects which lend themselves to briquetting withoutseizure with'the die and which may be sintered at relatively lowtemperatures at which the surface iron is most active in effectingbonding for instance 1300 to 1700 F.

A specific object of my invention is to provide individual particles offerrous metal with surface films o-r layers of ferrous sulfide (FeS)capable of effecting a scavenging action on adjacent iron oxide surfaceportions of the particles during sintering of products made from suchparticles as a result of which the ferrous sulfide (FeS) surfaceportions coalesce and form a liquid phase with theiron oxide .(Fe Osurface portions to produce to effect a reaction between the latter andthe pure iron or slightly oxidized iron surface portionsof'the'particles to form in situone or more films'or layers offerrous'sulfide adapted to inhibit new or additionaloxidati'onof suchiron surfaces of the particles during storage and to'serve as ascavenging and bond improving agent"dus ing sintering of a massof suchparticles.

ewsassa ings wherein:

apistonembodyingrmyinventiomrandl I indiizidualparticles- I I I appearfrom-the following deseriptionand from the draw- I g, I Figure 1;isanzelcvational view partly in section showing I II I Figure: 2. isIahighIy magnified view' typifying the in ternalr structure ofthe pistonof Figure 1 as evident from a 'photomicrograph. I I I I I I I II-ziii'a've discovered that-toobtainoptimum-1 distribution ofthe'ironsulfide in the particle mass 'andcoverage of' the individualparticles to resist. further oxidizing effects during storageand:enhance-the'extent' of scavenging action I during: sintering, theferrous particles should be treated i 1 i bysubjecting them at, 'roorntemperature-'on'wlziiletsuib ably heated to thevchemical action of .asulphur bearing I .gaseouscomppsition, preferably hydrogen sulfide: (HS);

I tHeatingt the particles is. advantageous; to increase the 3 I I tintensity ofchemicalreaction; I ;Agitation:ofthetparticles I is helpfulespecially whenytreatinga thezparticlesatroomf I temperatureOncontactofithehydrogentsulfide gaswitlr the: individual particles,a-reactio n occursrwitlr the: pure or} slightly I oxidized-iron,surfaces of the particles to I i I produce, in situ one or more integralprotective; and I $caveng ngfilmsoi' ferrous. sulfidendescribediabove-onthe a l The gaseous. treatment preferably carried out} im- Imedia-tely after. makingthe-particles.or ateantearly'period I Ithereaftento obtaintmaximum conversionzof-ithe ironzsui' sinteringa;

accordance with the invention and successfully made intoarticleshavingtsatisfactory properties; Theferrous metal particles mayalso containsmalliamounts of alloying: constituents-such. ascarbon,silicon, nickel, etc; Thus the particlesmaybe those offreducedmagnetite; low carbon steeh; low carbon atomized-iron, stainlessiron orsteel. The particulate ferrousinaterialfmay be treated by the hydrogensulfide in any suitable piece of equipment to effect the: formatio'nrofrironv sulfide on the surface of the particles. Thus-for example, theparticliesmay be placed as a loose mass on astray in'a. suitablyheate'dretort-type furnacehaving a frontal opening into whichhydrogensul fide gas may be introduced, filtered through the mass and beexhausted through another opening at the'back of the furnace; Suchretortmaybe housed in a=-hood equipped with a blower to exhaust'the gas fromthe-furnace and the-furnace will be'provided with a suitable temperaturecontrol and recording equipment to maintain uniform temperatures.Moreover'thetray may 'be agitated by a suitable :vibrator; Satisfactoryresults are obtained when thwpowders are treated at a temperaturein'theirange of 3759' F1 to 325"F. for periodsranging from S'to 25.minutesandwhereby th e'sulphurcontent' of the treated particles bychemical analysisis in'the range of 0' 275% fo0.325"%. v

Thus mill scale iron powder-havingtthe.following-screen analysis:

7 7 Percent Retained on .100. mesh; 12.8" Retained'o'nr 150. mesh .2l. IRetained on 200-mesh 1821 I I Retained onr250tmesh; 6 32'Retained:on;'325"mesh; s 13.9

Passed thru 325 mesh 2s faceportions totiron-sulfidebefore new'or'additiona'l iron I I I oxide-layers are:- formed onxthe: particlesurfaces by en'- 3 ;posure toair or;otheroxidizinginfiuenceszlnanyeventt' the; panielesshouldbe treated as zdescrilied 'prionto I thetopof. a rotating*tower suitably heated and having] an I outletiattlie'basefrom whiehztoremove:theipowdetafter I I treatment. Hydrogen sulfidegas' will be fed" into the tower atwthe l-owcr end through a suitableinlet and'xex I hausted-at the top through asuitableoutlet therefor; I IThe particles of particulate ferrous material treated I Iasdescribedabove and having the deposit of-ironsulfid'e formed} insitu'mayflthereafter" be advantageously com;- i I I I pasted, by: knownmeans and conventional briquetting,

andhaving;achemicalanalysis as follows:- I I Carbon .03 I I Manganese.36 t I I Phosphorous I salesmen"- y I '.0;1 I S l c -t--- -t--t 1 00:OXy'ge'm; j' 1.26

'I-ron remainder I when treated-as described in a retort furnacehaving-a 6" diameter opening and 14" long," for: a period of fifteenrate of.5.to 6 cu; ft. per hour to effect conversionof the iron. surfaceportions to iron-sulfide was capable of. handling-between6 to 10*lhs. ofmaterial for each v1 -5 minute II I period. A chemical analysis of thismaterialafter treatment showed a sulphur content-of between 0.275% to,0.30%.

The: increasezin weight'of a 80 gram sample of the-treated: I I ironpowder 'was',0;1 25-%'.' Based on-' a v mathematical I computation inwhich ,it' wasassumed that the: particles t I were spherical andperfectly homogeneous and wereyflG tt I I I indiametenthe deposit orcoating. produced'on the particles was" estimated to'be" approximately.00001".

:The time and temperature treatment of otheri'particulatel Iferrou'stmaterials may readily'zhe determined" in accordance,

particles,the particulate ferrous material mayj beifed into pressures'ofabout 30,000t0 60,000 psi. depending upon thedensity' desired to formdesired articles of commerce such as the pistons 'shown' inFigure landthe compacts sintered inta suitable furnace, for example an electricallyheated furnace having. means providing a controlled atmosphere thereinofthe exothermic type.

-As previously described, I have discovered that the surface'ironsulfide deposit or formation on the particles has-a scavenginga'ctionduringsintering of the compact causing-coalescence of the iron oxide andiron sulfideto form puregrain' boundaries between particles andboundaries comprising'iron oxysulfide to thus produce an .improvedmetallurgical bond between adjacent particles of thestructure.

This is evident in Figure 2 for example, where the scavenging eifect ofthe iron sulfide is apparent in the relatively clean1 grain boundariesillustrated at 4' and by the coalesced iron oxide and iron sulfideindicated at 5 in this figure; the areas of concentrated iron oxysulfidebeing indicated by' the stippling at 6 in this figure.

One of the advantages of the use of iron sulfide" bearing particles ofiron produced as above is the substantial saving in required kilowattpower consumption of the sintering furnaceand in its maintenance cost.He'retofiore it was necessary for example to sinter high grade ironparticles of electrolytically produced powder ata temperature ofapproximately 2050 F. By utilizing sucli iron particlesias treated inaccordance with the present invention compacts thereof may besuccessfully sintered at temperatures in therange of 1300 F." to 1700F;'best results being obtained in the" range 1550 F. to 1700' F. Th'esesame-low temperatures are likewise possible when employing other' iron'powders, even low grade mill scale iron powder"; I

Not only does the presence of .the' iron sulfide on the particles permitlower sintering temperatures and'iinprove Percent I particles prior toQbriquetting and sintering; Moreo er,

the metallurgical bond but there isalso a pronounced increase in thedegree of sintering that occurs at the lower s'intering temperaturesthan would be possible without the presence of the iron sulfide. This isonly possible because of the scavenger effect or coalescence describedabove effected by the iron sulfide on the iron oxides which inhibitsintering. In addition to the foregoing the coalescence eifect of thesulfide on theoxides in absorbing the same reduces the yield strength ofthe product in the as sintered condition because the oxide is then nolonger available to produce a precipitation hardening effect whichnormally exists in prior sintered iron masses in which the sulfide isnot present. This reduced yield strength material with its excellentductility makes it particularly suitable for coining and cold work- 4.As an articleoimanufactm'e a metal body .compris.

5. In a process of preparing particulateferrous metals for use in themaking of sintered products the improvement which consists inheatingsaid particles to a temperature in the. order of about 275? -to325 F., passing hydrogen sulfide gas through a loosemass of said ing bywhich techniques the yield strength for a given specific gravity may begreatly increased above those heretofore possible, and even doubledwhere such prop- Further increase in the ductility of the resultantsintered product of even in the case of electrolytic iron powder andcertain other iron powders has been found 'posfsible by the addition of0.5% to 1.5% by'weig-ht of ferric oxide in powdered form to the gas neatanen po additions of small amounts, for instance about 74% by weight ofstearic acid to the prior to briquetting are desirable as a lubricant.

Although my invention has been illustrated in conjunction with a piston3, it will be understood thatthe same is not limited to the making ofsuch articles but can be employed in the making of other articles and inthe making of various stock material from which articles are fabricated.Moreover, while the invention has been described utilizing hydrogensulfide gas as the agent for treating the ferrous particles it will beunderstood that some of the desirable effects of the invention althoughto a markedly lesser extent and with less uniformity may be obtained bydirectly adding to the powdered mass and thoroughly mixing therewith,prior to briquetting, from 0.5 to 5% by weight of powdered metallicsulfides. Examples of suitable additives are cupric sulfide, cuproussulfide, iron sulfide (FeS and FeS manganese sulfide, nickel sulfide,cuprous sulfide and nickel sulfide eutectic, cuprous sulfide and sodiumsulfide eutectic, cuprous sulfide plus metallic copper, nickel sulfideplus metallic copper, iron sulfide plus iron oxide and nickel sulfideplus iron oxide.

I claim:

1 As a product of manufacture a mass of individual powdered metalparticles for use in making sintered compacts, said particles comprisingferrous metal bodies hav ing integral chemically bonded surface films offerrous sulfide and said particles having a sulfur content between0.275% to 0.375% by Weight.

2. As a product of manufacture a mass of powdered metal particles foruse in making sintered compacts, said particles comprising ferrous metalbodies having integral surfacings of ferrous sulfide comprising thereaction product of said ferrous bodies and sulfur bearing compositionand said particles each having a sulfur content between 0.275% to 0.375%by weight.

3. As a product of manufacture a mass of powdered metal particles foruse in making sintered compacts, said particles comprising ferrous metalbodies having integral surface portions of iron oxide and furtherintegral surface portions of ferrous sulfide, said particles each havinga sulfur content in the range of about 0.275% to 0.375% by weight.

particles and effecting contact of said gas with the surfaces of saidparticles wherebyv to form by chemical reaction; of said gas on the.ferrous surfaces of said particles an integral layerof iron sulfide and.producetreated particles having a sulfur content in the range of 0.275%to 0.325% b tg i I 6. The method of making articles from particulatefer- ,rous metals having completely oxidized surface portionscomprisingiron oxide and having other surface portions comprising.substantially pure and slightly oxidized iron, comprising providing'aloose collection of said particles,

passing hydrogen sulfide gas through said mass ofipar ticles to effectcontact thereof with said'substantially pure and slightly oxidizedportions. of the surfacing of said particles whereby to produce bychemical action thereon integral films of iron sulfide, compacting.amassofIsaid treated. particles into a predetermined, form and heattreating said compact to effect a metallurgical bond". at adjacentsurfaces'ofsaid particles, the iron sulfide films of said particlesserving'during said. heat treatment to jefiectfa coalescence of thecompletely oxidized portions of said particle surfacing therewith intoiron oxysul-fide and the formation of clear grain boundaries. I

7. The method of making articles from particulate r rous metals jhavingcompletely oxidized surface portions comprising iron oxideand havingother surface portions comprising substantially pure and slightlyoxidized iron, comprising heating a loose collection of said particles,passing hydrogen sulfide gasthrough said mass of particles to effectcontact thereof with said substantially pure and slightly oxidizedportions of the surfacing of said particles whereby to produce bychemical action thereon integral films of iron sulfide, compacting amassof said treated particles into a predetermined form and heattreating said compact at a temperature between about 1300 F. to 1700 F,to effect a metallurgical bond at adjacent surfaces of said particles,the iron sulfide films of said particles serving during said heattreatment to effect a coalescence of the completely oxidized portions ofsaid particle surfacing therewith into iron oxysulfide and the formationof clear grain boundaries.

8. The method of making articles from particulate ferrous metalscomprising subjecting said particles to the action of a hydrogen sulfideatmosphere until an integral film of iron sulfide has been formed on theparticles by chemical reaction of said gas and the iron surfacing ofsaid particles, adding between about /2% to l /2% by weight of powderedferric iron oxide to said mass of particles and mixing therewith,compacting a mass of said mixed particles into predetermined form, andheat treating the compressed particle mass at a temperature between 1300F. to 1700 F. to metallurgically bond together adjacent surfaces of saidparticles, the said iron sulfide of said particles acting in response tosaid heat treatment to effect a coalescence of the iron oxide present atthe surfaces of said particles therewith.

9. In a process of preparing particulate ferrous metals for use in themaking of sintered products, the improvement which consists in heatingsaid particles to a temperature below about 325 F., and treating a loosemass of said particles with a sulphur containing composition "toefiect'contact of the latter with the surfaces 'of said particles-whereby toform an integral layer of iron=sulfide (Q11 atheferroussurfaces of theparticles by chemical reaction of said-composition withsaid'surfaces's'aid-particles having a sulfurcontent aftertreatmentof'between about "0.275 to 0.325% by weight.

"10. The method of -making articles :from particulate ferrous metalshaving completely oxidizedsurface-portions comprising-iron oxide andhaving other surface pordons comprising substantially pure and'slightlyoxidized iron, comprisingproviding a-loosecollection ofsaid particles,passing'hydrogen sulfide'gas through sa'id=mass of particles to effect"contact-thereof with said substantial- =ly pure and'slightlyoxidizedportions of'thesu'rfacin'g-o'f "said particles whereby toproduce "by' chemical action thereon integral films of iron sulfide,compacting a mass of said treated particles into a-predetermine d formand heat treating said compact at "a temperature "between about l300 to1700 to efiect a metallurgical bond at adjacentsurfaces of saidparticles, the iron sulfide films of 'said particles serving during saidheat treatment to effecta coalescence of the completely oxidizedportions'of said-particle surfacing therewith into ironoxysulfide 'and theformation of cleargrain boundaries.

I '11.'The process of making articles from particuiate ferrous metalscomprising mixing ferrous particles having completely oxidized surfaceportionscompris'in'g iron :oxide-with O:% -to 5% 'by 'weight of powderedmetallic sulfides, compacting a mass of said mixed particles into apredetermined form, and heat treating "the compressed 'particl'elmass ata temperature between about 130? F. to 1700 F. to metallurgically bondtogether adjacent surfaces of said particles with the sulfides acting inreproduce-by chemical'action thereon integral films 'of iron sulfide,mixing -with said particles 0.5% to 1.5% -by Weight of "ferric oxide,compacting amass of said mixed particles into a predetermined form andheat treating saidcornp-actat a temperature between about 1300 F. to1700 F. 'to e'tfect a metallurgica1 bond at adjacent surfaces of said;particles, the iron sulfide films of said particles serving during saidheat treatment to effect a coalescencethere'of with said ferric oxideintowiron oxysu'lfidetordmprov'ing the bond betweenthe particles and theformation of clear grain boundaries.

l3. Ina-process of-preparing particulate ferrousmetals Toruse in themaking of sintered productsthe improvem'ent'which consists in'heatingthe particles at a temperature of "about 300 F. for a period of aboutfifteen minutes while'treatingtheparticles withghydrogen sulfidewherebyto'etfectconversion of the iron surface portions 'toiron sulfide,'thesaid particles 'havinga sulfur content aftertreatmcnt of between0.275% to 0.30% "by weight.

14. The method of making articles from particulate ferrous metalscomprisingcompactinga mass of particles having completely oxidizedsurface portions comprising ironoxide and-having other surface portionscomprising integral 'films of iron sulfide into a predetermined form andheat treating said compact at a temperature between 1300 F.1to 1700 F.toeifect'a metallurgical bond at adjacent surfaces of said particles,the iron sulfide'films of said particles serving during said 'heattreatment to effect a coalescence of the completely oxidized portions ofsaid particle surfacing thcrewith'into iron oxysulfi'de andjtheformation of clear grain boundaries.

Conradson Jani 2;7, '1885 2,420,886 :Laifoon 'May 20, .1947

7 $791,561 -Beller May 7, 195-7 UNITED STATES PATENT OFFICE CERTIFICATE@F CORRECTION Patent No. 2,942,334 June 28, 1960 Roy E. Blue It ishereby certified that error appears in theprinted specification of theabove numbered patent requiring correction and that the said LettersPatent should read as corrected below.

Column 5, line 66 before "sulfur" insert a column 6, line 4, strike out"chemically bonded".

Signed and sealed this 31st day of January 1961.,

SEAL) Attest:

KARL H. AXLINE Attesting Oflicer ROBERT C. WATSON Commissioner ofPatents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.2,942,334 June 28 1960 Roy E. Blue It is hereby certified that errorappears in the-printed specification of the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 5, line 66 before "sulfur" insert a column 6, line 4, strike out"chemically bonded".

Signed and sealed this 31st day of January 1961a (SEAL) Attest:

KARL H. AXLINE ROBERT C. WATSON Attesting Officer Commissioner ofPatents

1. AS A PRODUCT OF MANUFACTURE A MASS OF INDIVIDUAL POWDERED METALPARTICLES FOR USE IN MAKING SINTGERED COMPACTS, SAID PARTICLESCOMPRISING FERROUS METAL BODIES HAVING INTEGRAL CHEMICALLY BONDEDSURFACE FILMS OF FERROUS